Simulation of Water Flow from a Percolation Test Hole in Layered Soil

Abstract

Abstract

In order to better explain problems in the correlation of percolation test and soil hydraulic conductivity data, a finite-element program (TWODEPEP) was used to solve Richards' water-flow equation in cylindrical coordinates. Both saturated and unsaturated aspects of water flow from a percolation test hole were simulated. Inputs for the simulation model were the soil hydraulic conductivity, which was measured using the Guelph permeameter technique, and water-retention data for each layer of a Monongahela silt loam soil (a fine-loamy, mixed, mesic Typic Fragiudult). Pressure-head distribution and rate of water flow were simulated. A thin (approximately 10-mm) saturated zone near the water source, approximated by the region inside the zero-pressure line, was nearly constant in size with time, but the wetting front continued to advance. It was also found that the horizontal movement of water in the soil was dominant over the downward vertical movement due to the movement of the water in both the upper and middle layer rather than the lower layer because the soil in these two layers was more permeable than the underlying layer. Simulated flow results agreed with the geometric mean of the field data obtained at six sites. The simulated results in the layered soil were compared with those in a uniform soil to show how soil layers significantly affect water flow from a percolation test hole.

Paper no. 8081 of the Journal Series of the Pennsylvania Agric. Exp. Stn., supported by Hatch Project 2764.

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